The present invention relates to treatment of a wastewater effluent prior to discharge into a stream or other suitable place. More specifically, this invention relates to treatment of wastewater containing bentazon.
The compound 3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide, hereinafter referred to by its common name of bentazon, and particularly salts thereof, is an effective herbicide. However, the wastewater obtained from preparing such products contains a small amount of bentazon or salt thereof which is not readily biodegradable. Before this wastewater can be discharged into the environment, bentazon must be reduced to an acceptable level regulated by the EPA. Presently bentazon is removed from the wastewater with activated carbon packed in a column. When saturated with organics, the spent carbon is removed and later recycled via thermal regeneration. This process requires continual replacement of the spent carbon bed.
Bentazon-containing wastewater which can be treated according to the invention is obtained when bentazon is extracted from solutions of the crude active ingredient in organic solvents. For example, U.S. Pat. No. 3,875,155 discloses a process of this type and the process of the instant invention is particularly suitable for treating wastewater resulting from the process of this patent.
It is a purpose of the present invention to eliminate or substantially reduce the bentazon content of the wastewater from such process so as to be able to discharge the wastewater into the environment.
One method of treating bentazon is disclosed in U.S. Pat. No. 4,451,378 which involves adjusting the pH of the wastewater to a pH in the range of 7.5 to 9.5, i.e. an alkaline pH, adding an alkali metal or ammonium salt of bentazon followed by heating and then lowering the pH to 1 to 3 whereupon the bentazon precipitates in free form and can be readily filtered off. This process, however, requires adding additional substantially pure bentazon and also the step of filtration. The process of the instant invention on the other hand does not require filtration and the treated wastewater may be discharged directly into the environment.
Comparative Example 1 of U.S. Pat. No. 4,451,378 discloses heating the waste water at a temperature of 99.degree. to 100.degree. C. without adding additional bentazon. However, the pH is alkaline, i.e. 8.5. While acid is then added it is in a second container where the temperature is 20.degree. C. The product was gelatinous and not filterable.
U.S. Pat. No. 4,402,837 discloses a process for treatment of waste liquid to prevent environmental pollution by subjecting the wastewater to a heat treatment. However, this is directed to a waste liquid containing nickel cyanide which is an entirely different impurity having entirely different properties.
Another patent of interest is U.S. Pat. No. 4,387,029 which relates to the processing of oxidation of a condensate obtained in urea production plants. The process is employed at an alkaline pH.
U.S. Pat. No. 4,216,088 treats phenolic waters formed in the manufacture of phenol formaldehyde resins and the mixture is heated in the presence of alkali.